what is the difference between blood and erythrocytes?

Erythrocytes are red blood cells -- one component among numerous cellular and acellular components.

Well blood contains both white and red blood cells.. but red are the ones you want to think about more. And there's no difference.The word Erythrocyte is just another word for Red blood cell. They contain Haemoglobinn that give the cell its red color and they carry oxygen through out and to the body.

"blood" refers to whole blood
erythrocytes are the red blood cell
hematocrite is the measure of the different components in whole blood
The hematocrit (Ht or HCT) or packed cell volume (PCV) or erythrocyte volume fraction (EVF) is the proportion of blood volume that is occupied by red blood cells. It is normally about 48% for men and 38% for women.[1] It is considered an integral part of a person's complete blood count results, along with hemoglobin concentration, white blood cell count, and platelet count.

In mammals, hematocrit is independent of body size.

The term "hematocrit" (British English: haematocrit) was coined in 1903. Its roots stem from the Greek words hema (Gr ?) - blood, and krites (Gr ), judge - meaning to gauge or judge the blood.